Magnesium(II) Complexes of the dpp‐BIAN Radical‐Anion: Synthesis, Molecular Structure, and Catalytic Activity in Lactide Polymerization

Abstract

AbstractReaction of (dpp‐BIAN)Mg(THF)3 (1) {dpp‐BIAN = 1,2‐bis[(2,6‐diisopropylphenyl)imino]acenaphthene} with one molar equivalent of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) proceeds with oxidation of the dpp‐BIAN dianion in 1 to the radical‐anion and affords the (dpp‐BIAN)Mg(TEMPO)(thf) (2) complex. The reaction of dpp‐BIAN with an excess amount of magnesium and 0.5 molar equivalents of I2 in Et2O gives (dpp‐BIAN)MgI(Et2O)n, which then reacts in situ with (Me3Si)2NK to produce (dpp‐BIAN)Mg[N(SiMe3)2](Et2O) (3). Solvent‐free magnesium amide (dpp‐BIAN)Mg[N(SiMe3)2] (4) was synthesized by treating equimolar amounts of MgI2, dpp‐BIAN, and sodium in toluene at reflux followed by treatment with (Me3Si)2NK. Deprotonation of diphenylacetonitrile with [(dpp‐BIAN)Mg(μ‐Me)]2 (5) produces keteniminate complex (dpp‐BIAN)Mg(N=C=CPh2)(Et2O) (6). Complexes 2–4 and 6 were characterized by ESR and IR spectroscopy; their molecular structures were determined by single‐crystal X‐ray analysis. Compounds 1–3 catalyze the ring‐opening polymerization of L‐ and rac‐lactides to give high molecular weight isotactic and stereoblock polylactides correspondingly.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)